1. Field of the Invention
The present invention relates to an organic light emitting display device and a method for fabrication of the same and, more particularly, to an organic light emitting display device with improved lifespan and luminance and a method for fabrication thereof.
2. Discussion of the Related Art
For an image display apparatus embodying a variety of information on a screen as an important technique in advanced information and communication, there is continuous progress in development of thin, light-weight and/or portable apparatuses with improved performance. With progress towards an advanced information society, there is a need for development of various display devices and, especially, a liquid crystal display (LCD), a plasma display panel (PDP), an electro luminescent display (ELD), a field emission display (FED), a vacuum fluorescent display (VFD), and the like are recently under active investigation and development. Among these, an organic light emitting display device is a flat display device with reduced weight and volume to eliminate weight and volume problems of a cathode ray tube (CRT) and controls a light emission amount of an organic emission layer so as to display an image and, therefore, draws remarkable attention in the related art.
An organic light emitting display device is a self-luminescent device using a thin light emission film between electrodes and may be manufactured into a thin product in a sheet form. An active matrix type organic light emitting display device (AMOLED) includes pixels composed of three color (R, G, B) sub-pixels formed in a matrix form to display an image.
Each of the sub-pixels may have an organic light emitting device (hereinafter, referred to as “OLED”) and a cell driving part independently driving the OLED. The cell driving part may have at least two thin film transistors and a storage capacitor in order to adjust an amount of current provided to the organic light emitting display device according to data signals, so as to control brightness of the organic light emitting display device.
A conventional OLED includes a cathode, an organic emission layer and an anode and, for a top emission type OLED, the cathode or anode composed of a transparent conductive layer is formed at a light emitting side. Here, the cathode or the anode at the light emitting side is placed over bottom layers. The cathode or anode composed of the transparent conductive layer has considerably high resistivity which in turn causes a voltage drop, that is, IR drop.
In particular, for a large screen, an area of the cathode or anode is also enlarged to increase a resistivity of the cathode or anode, thereby causing a significant IR drop in a length direction as shown in FIG. 1. Consequently, a display device with a cathode or anode composed of a transparent conductive layer aligned on a front side entails non-uniformity in luminance so that reliability of the display device is reduced.